The present invention relates to an intake manifold, for example, for use with motor vehicle engines.
The term "aluminum" as used herein and in the claims includes pure aluminum, commercial pure aluminum containing small amounts of impurities and aluminum alloys. The term "wrought aluminum" as used herein and in the claims refers to an article of aluminum prepared by plastic working. The term "center line average height" is used herein and in the claims according to the definition of JIS B0601-1982.
Conventional intake manifolds, for example, for use with motor vehicle gasoline engines equipped with an electronically controlled fuel injection system comprise a plenum and branch pipes and are entirely prepared by casting. With the cast intake manifold, however, it is impossible to reduce the wall thickness thereof below a certain limit owing to the flow characteristics of molten metal to be cast, so that the manifold has the problem of inceased weight. Further since the surface of the casting is rough and has voids, the casting must be finished to a smooth surface at least internally to decrease the air resistance for an improved intake efficiency. Thus, the manifold has the problem of necessitating a cumbersome finishing procedure. Moreover, since it is impossible to finish the entire inner surface of the manifold in view of its configuration, the air resistance still remains to be reduced to achieve a higher intake efficiency.
To solve this problem, we have already proposed the intake manifold disclosed in U.S. Pat. No. 4,829,944.
For improved performance, some motor vehicle engines having intake ports and exhaust ports are recently so adapted that at least the intake ports provided are two in number for each cylinder, and these ports are each provided with a valve. In this case, each intake manifold has connected thereto one branch pipe of the intake manifold, so that the number of branch pipes required is twice the number of cylinders, hence a large number of branch pipes. Because the engine rooms of motor vehicles are limited in size, the intake manifold must be compacted, whereas the increase in the number of branch pipes imposes a limitation on compacting.